1. Field of the Invention
The present invention relates to methods for adjusting the characteristics of dielectric filters such as dielectric duplexers and devices for practicing the methods.
2. Description of the Related Art
A conventional method (1) for adjusting the characteristics of dielectric filters is shown in Japanese Examined Patent Publication No. 7-52206, which provides a device in which the state values of elements disposed in a filter constituted of lumped-constant elements or distributed-constant elements are determined in such a manner that the difference between a value of measured vector information and a value calculated according to an equivalent circuit of the filter is as small as possible, and adjustments are made such that the determined state values of the elements coincide with targeted values. In addition, an article (2) titled xe2x80x9cON COMPUTER AIDED TUNING OF MICROWAVE FILTERS,xe2x80x9d IEEE Proc. ISCAS/76 introduces a device in which a target of (resonant frequency), used when a resonator is tuned by the characteristics of a reflection phase, is equivalent to the of of the filter. Furthermore, Japanese Unexamined Patent Publication No. 4-240901 (3) provides a device for trimming an electronic component in which changes in the characteristics with respect to the amounts of processing are memorized to update trimming conditions by using an average value of performance information obtained from the cumulative data.
Dielectric filters have a higher Q than surface acoustic wave filters or multi-layer substrate-type filters and have good temperature characteristics. Furthermore, in such dielectric filters, it is easy to make adjustments by a trimming process. As a result, the dielectric filters are suitable for applications requiring superior characteristics. However, it is difficult to apply the above-described conventional adjusting methods to the dielectric filters.
In other words, for example, as in the case of a basic low pass filter of the Chebyshev type, a filter-adjustment device described in (1) is usable when the equivalent circuit of the filter has a simple and clear configuration. However, it is difficult to make adjustments of filter characteristics in a short time in the case of a dielectric filter in which many elements of the equivalent circuit of the dielectric filter are influenced by adjusting a certain specified part.
The method for adjusting a filter described in (2) is a method of tuning conducted by using the fact that, in a case of a typical type of band pass filter (BPF), the pass phase between resonators is 90xc2x0 (the reflection phase is 180xc2x0). This method can be used in a Chebyshev-type BPF, and the like. However, the method cannot be used with a block-type dielectric filter having an attenuation pole outside a pass band, or when the BPF characteristics are changed.
The device for trimming an electronic component described in (3) is usable when the amounts of processing and the amounts of changing of characteristics are closely related by first-order expressions. However, regarding a dielectric filter in which a conductive film is formed on a dielectric block, it is impossible to adjust the characteristics only with the aid of approximate first-order expressions simply using average values, since the relationships between the amounts of processing and changes in the characteristics are complicated.
To overcome the above described problems, embodiments of the present invention provide a method for adjusting the characteristics of a dielectric filter, a method for adjusting the characteristics of a dielectric duplexer, and a device for adjusting the characteristics, in which specified characteristics can be easily obtained in a short time, even in the case of a dielectric filter in which there are complicated relationships between the amount that a specified part of a dielectric member or a conductive film is trimmed, and the corresponding changes in the characteristics, such as a dielectric filter and a dielectric duplexer produced by forming a conductive film on a dielectric block.
One embodiment of the present invention provides a method for adjusting the characteristics of a dielectric filter produced by forming a conductive film on a dielectric member, including the steps of: first, obtaining in advance data on the relationships between amounts of trimming and adjustment values, the data showing the relationships between the amounts of trimming a specified part of the conductive film or the dielectric member of a sample dielectric filter and changes in the adjustment values of a central frequency, a coupling coefficient between resonators, and the like; second, measuring the characteristics of a dielectric filter to be adjusted to obtain the adjustment values of the dielectric filter from the measured characteristics; third, obtaining a targeted amount of trimming the conductive film or the dielectric member based on both the difference between the adjustment values and targeted adjustment values and the data on the relationships between the amounts of trimming and the adjustment values; and fourth, trimming the conductive film or the dielectric member of the dielectric filter, based on the targeted amount of trimming.
In this way, in the first step, the relationships between the amount of trimming the dielectric member or the conductive film of the sample dielectric filter and the changes in the adjustment values of the central frequency, the coupling coefficient between resonators, and the like, are obtained. In the second step, the adjustment values of the filter are obtained from the characteristics of the dielectric filter to be adjusted. Third, the targeted amount of trimming the conductive film or the dielectric member is obtained from the targeted adjustment values and the data on the relationships between the amounts of trimming and the adjustment values. And fourth, the conductive film or the dielectric member of the dielectric filter is trimmed according to the targeted amount of trimming.
As a result, even in the case of a dielectric filter such as a dielectric duplexer, in which changes in a central frequency, a coupling coefficient, and the like, are influenced by trimming even one part, adjustments of the characteristics can be automatically and efficiently performed in a short time.
In addition, in the above described method, changes in the adjustment values of the dielectric filter caused by trimming of the conductive film or the dielectric member of the dielectric filter are obtained, to correct the data relating to the relationships between the amounts of trimming and the adjustment values. With this arrangement, when there are variations in the relationships between the amounts of trimming and the adjustment values in the dielectric filter, the data pertaining to the relationships between the amounts of trimming and the adjustment values in the sample dielectric filter is corrected when the dielectric filter is adjusted, with the result that the accuracy of the data showing the relationships between the amounts of trimming and the changes in the adjustment values is gradually enhanced.
In addition, in the above described method, the data on the relationships between the amounts of trimming and the adjustment values is expressed in terms of coefficients of functions expressing the changes in the adjustment values with respect to the amounts of trimming. With this arrangement, the functions can be easily expressed, and the correction of the data showing the relationships between the amounts of trimming and the changes in the adjustment values can also be facilitated.
Furthermore, in the above described method, the second step is repeated multiple times in such a manner that the amount of trimming the conductive film or the dielectric member at one time in the second step is smaller than the targeted amount of trimming. With this arrangement, excessive trimming can be prevented since gradual adjustments are performed until the targeted characteristics of the dielectric filter are obtained.
Furthermore, in the above described method, a ceiling value is set on the amount of trimming the conductive film or the dielectric member at one time in the second step or the targeted amount of trimming. With this arrangement, production of a dielectric filter incapable of being adjusted due to excessive trimming can be prevented.
Another embodiment of the present invention provides a method comprising the steps of: first, creating a database showing the relationships between the filter characteristics of a dielectric filter before adjustment, and the amount of adjustment of adjusted parts which are necessary to obtain a specified filter characteristic based on the initial filter characteristics, when the characteristics of the dielectric filter such as a dielectric duplexer are adjusted, and second, measuring the filter characteristics of the dielectric filter to obtain from the database the amount of adjustment corresponding to the filter characteristics, so as to be able to make adjustments according to the obtained amount of adjustment.
According to the above described method, the amount of trimming necessary to obtain the specified filter characteristic, given the initial filter characteristics of the dielectric filter before adjustment of its characteristics, is stored as a database in advance, and based on the database, the amount of adjustment is obtained according to the initial characteristics of the dielectric filter.
As a result, even when the equivalent circuit of the dielectric filter is complicated and many elements of the equivalent circuit are thereby influenced by the adjustment of one certain part, with the use of the relationships between the amount of actual adjustment and the changes in the filter characteristics of the dielectric filter, a desired filter characteristic of the dielectric filter can be reproduced with high precision, thereby leading to enhancement in the efficiency of adjustment of characteristics.
In addition, in the above described method, the relationships between the filter characteristics of the dielectric filter and the amount of adjustment obtained by the second step are entered in the database created by the first step. With this procedure, every time the characteristics of the dielectric filter are measured and adjusted, the content of the database is increased. Furthermore, it is possible to make adjustments with respect to a wide range of variations in the filter characteristics of the dielectric filter before adjustments of the characteristics.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.